Restoration of piers in Pearl Harbour
A hydrodemolition robot from Aquajet Systems is helping Triton Marine Construction to achieve remarkable production rates in the removal of spalled concrete from two piers at Pearl Harbour, in Oahu, Hawaii, USA. The Aqua Cutter HD-6000’s high-pressure water jet system takes just a minute to remove a cubic foot of the weak 1940s concrete – equivalent to a cubic metre in about half an hour.
“Its performance is incredible,” says Triton Marine Construction superintendent Brett Gordon. This is Triton Marine’s first project using its newly-purchased HD-6000 and other schemes are already lined up. “We feel that hydrodemolition will soon be specified on every job and we decided to purchase the equipment now so that we are set up for that movement into the future.”
Triton Marine, which is based in Bremerton, Washington, is working as subcontractor to Nova Group Construction to carry out renovations to Piers F12 and F13 on Ford Island at Naval Station Pearl Harbour. Areas of concrete were in poor condition and so are being replaced to provide a better surface and ensure the piers’ longevity. The work involves the removal of the spalled concrete and any corroded rebar followed by their replacement with new materials.
The Aqua Cutter HD-6000 robot was supplied to Triton Marine by Putzmeister America’s Water Technology Division, which also provided a two day course in its operation and servicing, followed by further training at the job site on Ford Island. “I am thrilled with Putzmeister and Aquajet,” says Gordon. “They have provided me with a good, reliable product.”
Triton Marine had previously always broken out concrete using labour-intensive conventional methods with hammers. The decision to buy the HD-6000 was taken with a view to forthcoming contracts, in particular a major highway project where time pressures will be intense. “We looked at the closures that will be allowed there and the manpower that would be needed for conventional methods,” says Gordon. “Hydrodemolition was the best way to go. We are also looking to the future. We feel that hydrodemolition will soon be seen as the only way to remove concrete. Any other method causes more damage to the concrete.”
Buying the Aqua Cutter HD-6000 for the Pearl Harbour project enabled the staff to build familiarity in its operation ahead of the more time-sensitive highway scheme. The work involves the removal of some 3,000 sq ft (280m2) of concrete from the decks of the two piers, in individual areas of varying shapes of typically 100 sq ft (9m2). It has been taking just one minute to remove an area of three square feet (0.27m2) to a depth of four inches (100mm), giving a rate of a cubic foot a minute or 1 m3 in just over half an hour. The first 110m2 phase of the project was completed over the course of a few days in January and the remainder is due to be carried out in March following the delivery of a vacuum truck for quick debris removal to keep pace with the Aqua Cutter.
“The concrete was originally poured in the 1940s, when specifications and quality control were a lot less stringent than today,” says Gordon. Over time, areas of the old reinforced concrete had become broken up, allowing the ingress of water.
The aggregate is a black, porous crushed stone, which is believed to be volcanic in nature. It gave a very soft concrete which the HD-6000 has been able to remove very quickly, says Eric Zimmerman, general manager of Putzmeister’s Water Technology division. “This is an exceptionally high production rate – about 3-4 times higher than normal,” he adds.
The HD-6000’s forward movement and the oscillation of its head can be easily adjusted to suit the area to be removed. In the weakest areas of the Pearl Harbour piers, only one or two passes of the high pressure jet head are needed to remove the concrete to the required depth.
Triton Marine staff quickly built up familiarity with the operation, gaining expertise in adjusting parameters such as the cutting width, speed and angle of the jet. “Setting up the machine very fast and very easy,” says Gordon. It took just two minutes from finishing one area to setting up for a neighbouring area that could be reached from the same set-up position of the high- pressure water pump.
The versatility of the HD-6000 avoids the unnecessary removal of sound concrete, adds Gordon. The passage of the jet is determined by adjusting the travelling range of the lance roller and the distance moved by the robot’s tractor unit. This ensures that the hydrodemolition is carried out only on the damaged concrete, without harm to the surrounding areas.
The Aquajet robot can be adjusted in moments to take account of the differing shapes and sizes of individual areas to be removed. Repairs were often much narrower than the width of the machine head but this was catered for using the HD-6000’s proximity switch adjustment which facilitates easy adaptation to suit varying widths. Magnetic stops determine how far the head goes before turning. The distance of tractor travel is also easily controlled, through visual markers set outside the removal area.
“Without these parameter adjustments, the movement time between patches would have increased and the overall production rate would have been greatly reduced,” says Zimmerman. “Also facilitating the high production rate was the flawless performance of the HD-6000.”